Particle accelerators



Oct. 7, 1969 w, F, G|BBQN$ ET AL 3,471,630

PARTICLE ACCELERATORS Filed Jan. 25, 1968 2 Sheets-Sheet 1 Inventors WF. G/BBo/ms K, h/ATKI V B M, 4,64% v da.

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Oct. 7, 1969 w GIBBONS ET AL 3,471,630

PARTICLE ACCELERATORS Filed Jan. 23, 1968 2 Sheets-Sheet 2 Inventor: W EGIBBO/VS WAT (Ml y [mt-n1, v M% United States Patent US. Cl. 17450.61Claims ABSTRACT OF THE DISCLOSURE A tubular chamber for a particleacceleratoris made from a number of sections each of which consists of ametal tube divided longitudinally into at least two members byelectrically insulating strips. The members are secured to the strips ina vacuum-tight manner.

This invention relates to particle accelerators of the type in whichcharged particles are accelerated along a curved or straight path in anevacuated tubular chamber. Such particle accelerators employing tubularchambers will hereafter be referred to as of the type specified andinclude accelerators of the betatron and synchrotron types employinggradually-increasing magnetic accelerating fields, and also linearaccelerators employing constant electric accelerating fields.

Where particle accelerators of the type specified are of large size, theevacuated tubular chamber is usually built up from a number of sectionsof electrically insulating material. An all-metal construction is notsuitable since this would allow electric currents to circulate withundesirable results.

Glass, ceramics, and epoxy resins are commonly used. A conductivecoating may be put onto the inner surface of some or all of the sectionsof the chamber. The coating inside each section is sometimes formed intwo electrically isolated parts so that it may be used for beamdeflection. The conductive coating may also be used to facilitate theremoval of any electric charge which may build up. Ceramic and glasschambers are very expensive because of the close dimensional tolerancesto which they must necessarily be made. Epoxy resin sections are cheaperbut suffer from the serious disadvantage that gases are evolved from theresin due to radiation produced by the charged particles beingaccelerated. This leads to defocusing of the beam of particles.

According to the present invention a tubular chamber for a particleaccelerator of the type specified includes a plurality of sections eachcomprising a metal tube divided longitudinally into at least two membersseparated from one another by strips of electrically insulating materialto which the members are secured in a vacuum-tight manner.

An embodiment of the invention will now be described with reference tothe accompanying drawings, in which:

FIGURE 1 is a transverse sectional view of an accelerator chamber;

FIGURE 2 is a side elevation view of part of one section of theaccelerator chamber of FIGURE 1',

FIGURE 3 is a longitudinal sectional view showing how two sections ofthe chamber are joined together; and

FIGURE 4 is a transverse view of part of FIGURE 3.

The drawings illustrate, not necessarily to scale, an embodiment inwhich a chamber section of elliptical crosssection is formed from twometal members joined along the major axis of the section.

3,471,630 Patented Oct. 7, 1969 Referring to FIGURES l and 2, two metalmembers 10 and 11 are each formed into an approximately semiellipticalshape as shown to form the main part of the section. outwardly-directedflanges are formed along the longitudinal edges of each section. The twosections are joined to two strips of ceramic material 12 and 13 by meansof intermediate U-shaped metal fillets 14, 15, 16 and 17, as shown inFIGURE 1. The'metal members must be joined to the ceramic strips in avacuum-tight manner so that the complete accelerator chamber may beevacuated. The four joints shown in FIGURE 1 are all made in the sameway, and that between metal member 10 and ceramic strip 12 will bedescribed in greater detail.

The upper surface of the strip 12 is covered with a metallised film andone side of the fillet 14 is brazed'to this film. The other side of thefillet 14 and the flange along one edge of the metal member 10 are thenwelded together.

Strengthening ribs 18 may be pressed into the metal members if required.

In order to simplify the connection of adjacent sections of the chamber,each end of a section has a ceramic endring 19 fastened to it. FIGURES2, 3 and 4 illustrate the method of attaching the end-ring to the metalmembers and ceramic strips. As shown in FIGURE 4, an end-ring 19, ofelliptical shape, has its side surfaces metallised as at 20, except fortwo small areas 21 on the major axis of the ellipse. The ends of eachmetal member are rolled back to form a flange, and these flanges arebrazed to the metallised areas of the end-ring as shown in FIGURE 3. Thenon-metallised areas 21 of the end-ring are provided so that the twometal members making up a section are electrically insulated from oneanother. The mechanical connection between the end-ring and the ceramicstrips must be made by using an epoxy-resin adhesive or a lowmelting-point glass.

FIGURE 3 also illustrates how two sections of the accelerator chamberare fastened together. To the side of each end-ring remote from themetal members is se cured, by brazing, a metal ring 22 of U-shapedsection. Two adjacent sections are fastened together by welding the twoadjacent metal rings together, as shown.

Since the complete accelerator chamber is in the form of a closed ring,then either each section will have to be slightly curved along itslength, or alternatively the curve may be formed by the connectionsbetween adjacent sections of the chamber. Electrical connections willhave to be provided between the metal members of some or all of thesections in order to facilitate charge removal. In the embodimentdescribed the two members of each section are electrically insulatedfrom one another. This is so that the two members of a section may beused as beam deflector plates when an electric potential is applied tothem and also to avoid encircling the varying magnetic field of theaccelerator with an electrically conduct- "ng path.

In some applications it is desirable to be able to heat the sections ofthe chamber. In such a case the metal members may be' made from ahigh-resistance material such as titanium or constantan, and they maythen be heated simply by the passage of an electric current through themembers. Ceramic materials have been mentioned as suitable for theinsulating strips. However, other materials, such as glass, are alsosuitable. The important consideration is that it must be possible toform a vacuumtight seal between the insulating strips and the metalmembers. I

The accelerator chambers of particle accelerators of the type specifiedare usually of elliptical cross-section, but this is not essential, andchambers of different crosssection may be made.

The methods described of forming the joints between the metalmembers,the ceramic strips and the end-rings are only by way of example,and other methods are known to those skilled in the art.

The main advantage of sections made in accordance with the invention istheir relatively low cost and simplicity of manufacture. The metalmembers and fillets are easily formed, and the only complexityintroduced 1's in the forming of the seals between metal and ceramiccomponents.

. What we claim is:

: 1. A tubular chamber for a particle accelerator of the type specifiedwhich includes a plurality of sections each comprising a metal tubedivided longitudinally into at least two members separated from oneother by strips of electrically insulating material, each member beingsecured to each insulating strip in a vacuum-tight manner by means of anintermediate metal fillet individual to that member.

2. A chamber as claimed in claim 1 in which each section of the chamberhas an end-ring of electrically insulating material secured to each end.

3. A chamber as claimed in claim 2 in which the endrings of two adjacentsections are secured to one another by means of intermediate metalfillets.

4. A chamber as claimed in claim 1 in which said electrically insulatingmaterial is a ceramic material.

5. A chamber as claimed in claim 1 in which the members are made from ametal having a high electrical resistance.

References Cited UNITED STATES PATENTS 2,775,643 12/1956 Scott.

LEWIS H. MYERS, Primary Examiner D. A. TONE, Assistant Examiner US. 01.x.R. 313-317; 328-256

